1. Technical Field
The present invention relates to an organic electroluminescent display (OELD) device, more particularly, to a dual panel type OELD device and a method of fabricating the same.
2. Related Art
An OELD device of new flat panel display devices is a self-emitting type. The OELD device has excellent characteristics of viewing angle, contrast ratio, and so on. Also, since the OELD device does not require a backlight assembly, the OELD device has low weight and low power consumption. Moreover, the OELD device has advantages of high response rate, low production cost, and so on.
FIG. 1 is a circuit diagram showing a pixel region of the related art OELD device. As shown in FIG. 1, a gate line “GL”, a data line “DL”, a power supply line “PL”, a switching thin film transistor (TFT) “STr”, a storage capacitor “StgC”, a driving TFT “DTr”, and an organic electroluminescent diode “E” are formed in one pixel region “P”. The gate line “GL” and the data line “DL” cross each other such that the pixel region “P” is defined, and the power supply line “PL” is formed to be parallel to the data line “DL”. The switching TFT “STr” is formed at crossing portion of the gate and data line “GL” and “DL”. The driving TFT “DTr” is electrically connected to the switching TFT “STr”.
The driving TFT “DTr” is electrically connected to the organic electroluminescent diode “E”. In more detail, a first electrode of the organic electroluminescent diode “E” is connected to a drain electrode of the driving TFT “DTr”, and a second electrode of the organic electroluminescent diode “E” is connected to the power supply line “PL”. The power supply line “PL” provides a source voltage to the organic electroluminescent diode “E”. The storage capacitor “Cst” is disposed between gate and source electrodes of the driving TFT “DTr”.
When a signal is applied to the switching TFT “STr” through the gate line “GL” such that the switching TFT “STr” is turned on, a signal from the data line “DL” is applied to the gate electrode of the driving TFT “DTr” such that the driving TFT “DTr” is turned on. As a result, light is emitted from the organic electroluminescent diode “E”. In this case, when the driving TFT “DTr” is turned on, a level of an electric current applied from the power supply line “PL” to the organic electroluminescent diode “E” is determined such that the organic electroluminescent diode “E” can produce a gray scale. The storage capacitor “StgC” serves as maintaining the voltage of the gate electrode of the driving TFT “DTr” when the switching TFT “STr” is turned off. Accordingly, even if the switching TFT “STr” is turned off, a level of an electric current applied from the power supply line “PL” to the organic electroluminescent diode “E” is maintained to next frame.
Array elements, for example, the TFTs, and the organic electroluminescent diode including an anode, a cathode and an organic emitting layer are formed on a single substrate. Alternatively, the array elements and the organic electroluminescent diode are formed on different substrates and a connection electrode for connecting the array elements and the organic electroluminescent diode is further formed. The latter may be called as a dual panel type OELD device.
FIG. 2 is a cross-sectional view showing one pixel region of the related art dual panel type OELD device. In FIG. 2, a gate line (not shown) and a data line 15 are formed on a first substrate 10. The gate line and the data line 15 cross each other to define a pixel region. A switching TFT (not shown) and a driving TFT “DTr” are formed in the pixel region. A passivation layer 25 covering the switching TFT and the driving TFT “DTr” is formed. The passivation layer 25 includes a contact hole 27 exposing a drain electrode 20 of the driving TFT “DTr”. A connection electrode 35 connected to the drain electrode 20 of the driving TFT “DTr” through the contact hole 27 is formed on the passivation layer 25.
In addition, a first electrode 53 is formed on a second substrate 50. A buffer pattern 57 corresponding to boundaries of the pixel region is formed on the first electrode 53, and a column spacer 55 is formed on a portion of the pixel region. A wall 60 having a reverse-taper shape with respect to an inner surface of the second substrate 50 is formed on the buffer pattern 57. Moreover, an organic emitting layer 65 and a second electrode 70 are formed on the first electrode 53. The organic emitting layer 65 and the second electrode 70 are respectively isolated from those in adjacent pixel region. The first electrode 53, the organic emitting layer 65 and the second electrode 70 constitute an organic electroluminescent diode “E”. The second electrode 70 contacts the connection electrode 35 on the first substrate 10 such that the organic electroluminescent diode “E” is electrically connected to the driving TFT “DTr”.
A seal pattern (not shown) is formed on edges of one of the first and second substrates 10 and 50 for sealing an inner space between the first and second substrates 10 and 50. The inner space of the first and second substrates 10 and 50 is filled with an inert gas or has a vacuum condition to preventing from being damaged by moisture or air.
In a fabricating process of the dual panel type OELD device 1, particularly, the second electrode 70 in one pixel region should be isolated from that in adjacent pixel region. To obtain this structure, the wall 60 having a reverse-taper shape is formed of an organic insulating material on the second substrate 50. One end, which is closer to the second substrate 50 than the other end, of the wall 60 has a first cross-sectional area smaller than a second cross-sectional area of the other end. The wall 60 surrounds each pixel region. An organic emitting material and a metallic material are sequentially coated and deposited on the second substrate 50, where the wall 60 has been formed, to form the organic emitting layer 65 and the second electrode 70.
However, the wall 60 and the column spacer 55 for the dual panel type OELD device are formed by different process such that one more mask process is required. In addition, since there is a continuous metal pattern 73 on the wall 60, there is a brightness problem due to particles. Moreover, since the driving TFT “DTr” on the first substrate 10 and the organic electroluminescent diode “E” have a point contact with the column spacer 55, a possibility of a contact problem is increased.
To overcome these problems, a spacer-free type OELD device including a dual-structured wall, which serves as a connection electrode, without the column spacer is introduced. Unfortunately, there is still a problem. Since the second electrode of the organic electroluminescent diode continuously formed on the dual-structured wall is used as a connection electrode, a planarization layer is required over the second substrate to obtain an uniform height of the dual-structure wall. When the planarization layer formed of an organic insulating material is heated, a gas is generated from the planarization layer. When the organic emitting material of the organic emitting layer is exposed to the gas, a thermal degradation is generated in the organic emitting layer such that a lifetime of the OELD device is reduced. In addition, a control of a contact area between elements on the first and second substrates of the spacer-free type OELD device is impossible.